1. Field of the Invention.
This invention relates in general to an Attachment Unit Interface (AUI), and more specifically to an Attachment Unit Interface (AUI) which may be selectively switched between a Media Attachment Unit (MAU) mode and a Data Terminal Equipment (DTE) mode.
2. Description of Related Art.
The communications industry has experienced phenomenal growth over the past several years. Much of this growth has occurred in the area of data communications involving computers and computer generated or stored data. The exchange of messages and data has been facilitated by the advent of local and metropolitan area networks. Remotely located computer users communicate over the local and metropolitan area networks to access data and to communicate with other remote computer users.
This phenomenal growth has led to new integrated circuits to support data communication applications. Nevertheless, in the marketing of highly-integrated, application-specific integrated circuits, targeting the needs of all customers is becoming increasingly difficult. To successfully sell a product in today's competitive marketplace, a chip manufacturer must create a distinct "feel" to their product through its form and function.
One way of creating a distinct "feel" to a chip is to design in flexibility. An integrated circuit manufacturer can attempt to anticipate all of the demands of its customers by designing multiple modes of operation into their chip. These modes are usually selected through configuration pins which are dedicated to mode selection. Thus, some pins may be used for mode selection during normal operation of the chip. For highly integrated designs, the pins of a device are usually all used; there are very few which are unconnected. Pins are used as functional inputs and outputs during normal operations. Further, since there are only a limited number of pins on a given package, they come at a premium. It is sometimes hard to give up a pin for defining configurations. Hence it is desirable to be able to configure a device's operation without having to sacrifice a pin which could otherwise be used as a functional input or output.
In network applications, nodes may be connected to a bus and have multiple, or concurrent, access to the communications medium. Control techniques are used to allow access to the communication medium and to resolve contention between the various users. Typically, a carrier sense, multiple access with collision detection (CSMA/CD) scheme is used. With CSMA/CD a node listens for activity and begins sending message packets when the node determines that no activity is occurring over the network. Sometimes simultaneous transmission by multiple nodes occurs. This results in collisions between the different message packets. When a node detects a collision, a signal is sent over the network to the other transmitting nodes. The affected nodes terminate their transmissions and probabilistically reschedule their next attempt to transmit.
The standard for Local and Metropolitan Area Network technologies is governed by ISO/IEEE 8802.3-1994. ISO/IEEE 8802.3-1994 describes the relationship among the family of 802 standards and their relationship to the ISO Open System Interconnection Basic Reference Model and is herein incorporated by reference. ISO/IEEE 8802.3-1994 defines the standards for a bus utilizing collision sense multiple access/collision detection (CSMA/CD) as a data link access method and is herein also incorporated by reference.
Typically, unshielded twisted pair cables or existing telephone wiring is used as the transmission medium to provide an economical solution to networking. However, the quality of the signals transmitted over unshielded twisted pair cables degradates as the distance between data terminal equipment becomes greater. Thus, repeaters are used to facilitate greater distances and to improve signal quality.
In the past, repeaters were limited to a fixed number of ports thereby limiting the number of data channels. Accordingly, repeater manufacturers designed hardware which could be cascaded so that multiple repeater circuits could be integrated into a single hub.
FIG. 1 illustrates the physical layer partitioning relationship 10 for interconnecting a repeater to a data source such as an Ethernet adapter on a personal computer or to another repeater. The physical layer contains the AUI interface 12. The AUI interface is a non-specific media interface. From the AUI interface, repeaters traditionally have internal MAUs 14 which allow them to connect to specific types of media such as twisted pair (i.e., 10Base-T).
Nevertheless, in all prior implementations of the AUI interface, the interface is exclusively that of a DTE. Interconnection to the transmission media are made via an external MAU through the AUI port. This approach is embodied in the original concept of the AUI interface as defined in the ISO/IEEE 8802.3-1994 standard referenced above.
This approach provides the end user flexibility since the type of media used for a Local Area Network (LAN) can be made independently of the underlying adapters and repeaters used in the LAN. While repeaters contain internal MAUs which are used to connect to specific types of media, AUI ports provide a medium non-specific interface to MAUs. MAUs may be purchased to connect to a type of media not addressed by the repeaters internal MAUs. To connect a repeater to the DTE port of a data source such as an Ethernet adapter card used on a personal computer or inter-repeater involves the connection of a DTE port to a DTE port.
FIG. 2 illustrates a repeater 20 having an AUI interface 24 and four twisted-pair ports 70. However, a generic data source having a DTE port cannot be connected directly to the repeater AUI interface implementing as a DTE port. External MAUs must be attached to both DTE ports with some medium type connecting the two MAUs. Alternatively, a DTE port of a data source may be connected to a twisted-pair MAU. The twisted-pair MAU may in turn be connected to one of the twisted-pair ports of the repeater. This configuration may be reversed if the data source includes a twisted-pair port. Further, if the data source includes a twisted-pair port, a third alternative connection may be implemented by directly connecting the twisted-pair port of the data source to one of the twisted-pair ports of the repeater.
Accordingly, the third alternative connection is the least expensive since an external MAU is not required. However, this is often the least desirable configuration since twisted pair ports are used, for a variety of reasons, much more often than the AUI ports.
It can therefore be seen that there is a need to change the mode of the AUI port from a DTE mode to a DCE or MAU mode. However, the DTE functions of the AUI cannot be eliminated.
It can therefore be seen that there is a need to provide a system for operating with a number of selectable modes of operation and yet be efficient from a logic and circuitry perspective.
It can also be seen that there is a need for an inter-repeater having an AUI port with selectable functionality.
It can also be seen that there is a need for an inter-repeater with an AUI port that can be selectively changed by the user to be an MAU port.
It can also be seen that there is a need to select between the MAU and DTE modes of operation for an AUI port via a single control signal, which may be accessible by any means including, but not limited to external sense pins or internal registers.